Impairments in social emotional reciprocity are among the core symptoms of autism spectrum disorders. Recent scientific and technological advances in the genetics of complex diseases and quantitative trait analysis, the emergence of the social and affective neurosciences, the measurement of heterogeneous behavioral phenotypes and quantitative traits associated with autism, and renewed attention to the developmental nature of neurodevelopmental disorders provide the foundation on which we have built our integrated, multidisciplinary research programs, addressing this defining feature of autism and potential treatments. This multi-site application for a STAART Center focuses on the central theme of social and affective processes in autism. Major institutions in Boston (Boston University School of Medicine, Tufts New England Medical Center, Harvard/Massachusetts General Hospital), northern New England (Dartmouth Medical Center) and Wisconsin (Waisman Center/University of Wisconsin) will collaborate on five projects that explore the early developmental course viewed within the context of family influences (Project I), underlying genetic causes using a quantitative trait approach (Project II), brain pathology and functioning (Projects III and IV), and treatment (Project V) of the core symptoms of social emotional impairment, and co-occurring affective disorder and problem behaviors in autism. The projects will be supported by a Clinical Core (Core B), which will collect diagnostic and phenotype data, DNA, and other biological information from children with autism and their first degree relatives; and a Data Management and Statistics Core (Core C), that will create and manage the database and provide major support for data entry, access, and statistical analyses for the projects. The Administrative Core (Core A) will coordinate the scientific components of the Center including the projects and other Cores, and will foster the development of new educational, clinical, training, and other outreach programs for the local, regional and national autism community. Our center brings together a team of leading scientists drawn from a broad geographical base who together create the infrastructure needed to fulfill the mission not only for our own scientific programs but also for the collaborative research that will be an important part of the NIH STAART Centers Program.